When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi all. Making this post for those that find brake fluid seeping/leaking around the cap. I actually did this last summer, but just remembered to make a post about it now. Maybe this could help you out.
I noticed last year that, no matter how well I cleaned up after bleeding/flushing/filling my brake fluid, I would still find some brake fluid around the cap of the reservoir. It didn't matter if the fluid level was at the FULL mark or half way mark, I would still see fluid there. It may not be a big deal to some, but I would prefer not to have any amount of brake fluid where it's not meant to be.
I can't remember exactly where, but it was probably from the forum and/or one of the google searches that lead to me replacing the gasket. Fortunately, it was a simple fix for me. And since the new gasket, I haven't seen any fluid there. I've done a few cruises and 2 track days and no fluid seeping there. I am unsure if it's the same cap/gasket for a z06 and a c5 coupe. Mine is a '02 z06
Thanks!
I would usually see some fluid right below the cap, by the reservoir threads. Right about there is where I would see the fluid. Picture of my old gasket, you can see how it's become bubbly around it. You can seen the little slit(for ventilation) on the original gasket. Picture of my old gasket extended. Reservoir cap with the gasket removed. The new Dorman gasket did not have the little slit for the ventilation. So, I went ahead and made a ventilation slit myself. Picture of the new gasket on the same old cap. Purchased at a local autozone, but can be found online as well. Dorman 42072.
The brake fluid is in a sealed system. The reason being, brake fluid absorbs moisture in the air. The rubber bladder or diaphragm in the cap expands and contracts to make up for drop in fluid when braking and expansion and contraction from temp changes, this keeps the fluid separated from the outside air. Yours may have been leaking because of the hole in the rubber diaphragm and the new cap did not have a hole because it isn't supposed to and do not overfill the master cylinder so the diaphragm can do it's job. The brake fluid should not be vented to the outside. It won't last long if it is.
Maybe I shouldn't have used the word ventilation as I totally agree with you that the brake hydraulic system is indeed sealed. Otherwise, it would be a big problem.
And I didn't even know about the gasket until i searched for leaking m/c caps. Once I removed my old gasket, i saw that it did have a slit so I made the slit to my new gasket as well. And both of the gaskets expand, but the new one does not leak. As noted in that thread, isn't the slit already there to begin with? Now I'm a bit confused. I can buy another gasket and see if it makes a difference. But I haven't had any leaks or difference in braking since I put it on.
Originally Posted by JR-01
The brake fluid is in a sealed system. The reason being, brake fluid absorbs moisture in the air. The rubber bladder or diaphragm in the cap expands and contracts to make up for drop in fluid when braking and expansion and contraction from temp changes, this keeps the fluid separated from the outside air. Yours may have been leaking because of the hole in the rubber diaphragm and the new cap did not have a hole because it isn't supposed to and do not overfill the master cylinder so the bladder can do it's job. The brake fluid should not be vented to the outside. It won't last long if it is.
Maybe I shouldn't have used the word ventilation as I totally agree with you that the brake hydraulic system is indeed sealed. Otherwise, it would be a big problem.
And I didn't even know about the gasket until i searched for leaking m/c caps. Once I removed my old gasket, i saw that it did have a slit so I made the slit to my new gasket as well. And both of the gaskets expand, but the new one does not leak. As noted in that thread, isn't the slit already there to begin with? Now I'm a bit confused. I can buy another gasket and see if it makes a difference. But I haven't had any leaks or difference in braking since I put it on.
The diaphragm will not function as designed if there is a hole in it. It will not fill the vacuum created by drop in fluid, or contract when fluid expands. Air will just flow in and out and you don't want that.
I can't say I paid attention to the diaphragm everytime I opened the m/c cap, but there were times when it was extended and times where it was just on flat. I can't see how my previous diaphragm developed a perfect clean slit like it had. The cars been tracked by previous owners, so I can see the bubbles developed from hot brake fluid possibly. I've done a bit more googling and found the same concerns on a camaro forum as well. Various people also state the slit is on the original diaphragm and various others also say theirs don't. No solid conlusion on either CF or the camaro forum.
links below for those who are interested in reading.
Now I'm even more curious, whoever reads this should go see if there is a slit on the diaphragm.
Originally Posted by JR-01
The diaphragm will not function as designed if there is a hole in it. It will not fill the vacuum created by drop in fluid, or contract when fluid expands. Air will just flow in and out and you don't want that.
Yea, who knows.
I use my car mainly for hpde and inspect the car and fluids during and after each event, so it may not be a problem. I just didn't want any brake fluid seeping out.
Originally Posted by helga203
From my understanding he said over time your system might be compromised.
I was having issues, late last year/early this year, with my brake fluid discoloring, which is usually an indication of moisture in the master cylinder. It shouldn't be an issue for my car, as I change the fluid every year. After a little investigation, I found a small hole in the gasket.
The diaphragm is there to take up the space of the fluid. If there is a split in it, the fluid will seep through instead. I would suggest that the small groove in the cap is to allow air pressures to be regulated.
The diaphragm is there to take up the space of the fluid. If there is a split in it, the fluid will seep through instead. I would suggest that the small groove in the cap is to allow air pressures to be regulated.
01-19-2019, 09:17 PM
Is Your Brake M/C Cap Seeping/Leaking Fluid?
